It is known to use a ureteral access sheath for creating an access channel from the external meatus to a location within the ureter of a patient to perform surgical procedures within the ureter and/or kidney. With an established channel to the ureter, a surgeon is able to insert and to withdraw a ureteroscope or other instrument more rapidly and with limited trauma to a patient's urinary system.
A typical prior art ureteral access sheath includes two subassemblies: a dilator and a sheath. The dilator is placed within the sheath, and the dilator and sheath combination is advanced through the urethra, through the bladder, and to the ureter. The dilator is then withdrawn, leaving the sheath in place. A ureteroscope is then advanced through the sheath to access the ureter.
A problem with known prior art ureteroscopic procedures concerns the need to irrigate the target site. Irrigation is critical during most ureteroscopic procedures. Since the inability to view the surgical area could have devastating effects, a procedure will not be continued until adequate viewing is achieved. Typically, irrigation fluid is supplied through the working channel of the ureteroscope. Because other instruments (i.e., a stone basket, grasper, laser fiber, etc.) also occupy the working channel, the flow rate of the irrigation fluid is reduced in proportion to be diameter of the instrument being used. Thus it would be desirable to provide a surgical environment in which the flow rate of irrigation fluid is not restricted by the presence of instruments within the working channel of the ureteroscope.
An additional problem with known prior art ureteral access sheaths concerns the need for guidewires in conjunction with the placement of the sheath. To use a typical prior art ureteral access sheath, the physician performs the following steps:                1. A cystoscope is inserted into the patient's urethra and advanced into the bladder, where the ureteral orifices are identified.        2. Using the cystoscope, a guidewire is inserted into the ureteral orifice.        3. Using fluoroscopy, the proximal end of the guidewire is inserted through the ureter and into the kidney.        4. With the guidewire carefully held in place, the cystoscope is removed over the guidewire.        5. The dilator is placed within the sheath.        6. The distal end of the ureteral access sheath is now back-loaded onto the proximal end of the guidewire and advanced over the guidewire and into the ureter. Advancement and position of the ureteral access sheath is usually verified with fluoroscopy.        7. The dilator is removed from the sheath.        
Now the sheath is in place to provide a working channel from outside the patient to the ureter. However, on occasion a surgical procedure may inadvertently puncture or lacerate the ureter. Normally, a secondary “safety wire” has been placed for access, in the event the access sheath needs to be adjusted or otherwise removed.
The safety wire is normally placed alongside the sheath. Placement of the secondary safety wire requires a number of additional steps:
                8. The safety wire is inserted into the lumen of the sheath and advanced into the kidney.        9. With both the original guidewire and the safety wire held in place, the sheath is removed.        10. The dilator is placed into the sheath.        11. The sheath is back-loaded onto the initial guidewire as explained before and advanced into the ureter.        12. The dilator is removed from the sheath.        
At this juncture, the sheath is in place, the original guidewire is disposed within the sheath, and the safety wire runs along the outside of the sheath. However, because the original guidewire occupies the same channel of the sheath into which the ureteroscope will be inserted, the original guidewire must now be removed before a surgical procedure can be commenced. Hence,                13. The guidewire is removed from the sheath.        
As can be seen, the requirement for a safety wire located outside the working channel of the sheath adds a number of steps and additional time and complexity to the procedure of positioning the sheath. In addition, the presence of the safety wire within the ureter alongside the sheath increases the possibility of lacerating the ureter.
In addition, some surgical procedures require the removal from the ureter of objects that are larger than the lumen of the sheath. In such instances, the objects are grasped against the distal end of the sheath, and the sheath must be completely withdrawn from the patient to extract the object. The sheath may be repositioned by once again placing the dilator into the sheath and advancing the sheath over the safety wire. However, there is now no safety wire running alongside the sheath. To position another safety wire alongside the sheath, the sequence of steps previously set forth must be repeated.
Thus there is a need for a ureteral access sheath which minimizes the number of steps required to position the sheath.
There is a further need for an improved ureteral access sheath which facilitates the placement of a safety wire.